CN113155967A - Phased array nonlinear laser ultrasonic detection system - Google Patents
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/041—Analysing solids on the surface of the material, e.g. using Lamb, Rayleigh or shear waves
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
- G01N29/043—Analysing solids in the interior, e.g. by shear waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/221—Arrangements for directing or focusing the acoustical waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2418—Probes using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/24—Probes
- G01N29/2437—Piezoelectric probes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/22—Details, e.g. general constructional or apparatus details
- G01N29/26—Arrangements for orientation or scanning by relative movement of the head and the sensor
- G01N29/262—Arrangements for orientation or scanning by relative movement of the head and the sensor by electronic orientation or focusing, e.g. with phased arrays
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
- G01N29/4472—Mathematical theories or simulation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
- G01N2021/1706—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/028—Material parameters
- G01N2291/0289—Internal structure, e.g. defects, grain size, texture
Abstract
The invention relates to a phased array nonlinear laser ultrasonic detection system, which comprises a mobile platform used for placing a workpiece to be detected, and also comprises: the laser ultrasonic transmitting system transmits laser to a workpiece to be detected to form a phased array scanning path formed by point light sources so as to finish deflection and focusing of ultrasonic sound beams at any angle; the ultrasonic receiving system receives an ultrasonic sound beam signal sent by the laser ultrasonic transmitting system and sends the signal to the control and signal processing and analyzing system; and the control and signal processing and analyzing system controls the laser ultrasonic transmitting system and the mobile platform and processes the received signals to realize defect detection. Compared with the prior art, the method has the advantages of more comprehensive and accurate detection, capability of realizing weak signal detection, more convenient and faster operation and the like.
Description
Technical Field
The invention relates to the technical field of nondestructive testing of workpieces, in particular to a phased array nonlinear laser ultrasonic testing system.
Background
The nondestructive testing is to measure the variation of the material to be tested due to the existence of defects by means of physicochemical means and modern instruments on the basis of not destroying the performance of the material to be tested. And judging whether the measured object has internal or surface defects or not according to the measurement result of the variable quantity. With the continuous progress and development of economic science and technology in China, the monitoring requirements on the mechanical property, the service life and the like of the material are more and more strict, effective nondestructive testing evaluation can improve the quality of the product and guarantee efficient and safe production, and better economic benefit is brought to enterprises. The conventional ultrasonic detection can only display an A scanning signal, and the detection result is not visual and insensitive to microdefects. Therefore, the phased array technology and the laser technology are introduced into the ultrasonic detection to derive ultrasonic phased array nondestructive detection, laser ultrasonic nondestructive detection and phased array laser ultrasonic second harmonic nondestructive detection, however, the detection sensitivity of the normal laser ultrasonic nondestructive detection to the micro defect or the closed defect is very low or even can not be detected, and the imaging resolution is not high, so that the problem can be perfectly solved by introducing the second harmonic technology, the second harmonic detection can not only accurately detect the closed micro crack, but also greatly improve the imaging resolution.
Disclosure of Invention
The present invention is directed to overcoming the above-mentioned drawbacks of the prior art and providing a phased array nonlinear laser ultrasonic inspection system.
The purpose of the invention can be realized by the following technical scheme:
a phased array nonlinear laser ultrasonic detection system comprises a mobile platform used for placing a workpiece to be detected and:
the laser ultrasonic transmitting system transmits laser to a workpiece to be detected to form a phased array scanning path formed by point light sources so as to finish deflection and focusing of ultrasonic sound beams at any angle;
the ultrasonic receiving system receives an ultrasonic sound beam signal sent by the laser ultrasonic transmitting system and sends the signal to the control and signal processing and analyzing system;
and the control and signal processing and analyzing system controls the laser ultrasonic transmitting system and the mobile platform and processes the received signals to realize defect detection.
The laser ultrasonic transmitting system comprises a high-frequency optical fiber pulse laser, a beam splitter, a phase controller and a scanning voltage controller, wherein the high-frequency optical fiber pulse laser is connected with the beam splitter, the beam splitter is connected with the phase controller, one end of the scanning voltage controller is connected with the phase controller, and the other end of the scanning voltage controller is connected with a control and signal processing analysis system. The high-frequency optical fiber pulse laser excites a laser beam, divides the laser into a plurality of light paths through a beam splitter, is controlled by a phase controller and a scanning voltage controller, and excites the pulse excitation at the same delay time to form a phased array scanning path formed by point light sources so as to finish the deflection and focusing of ultrasonic sound beams at any angle.
The ultrasonic receiving system comprises a piezoelectric sensor, a charge amplifier and a high-speed data acquisition card, wherein the piezoelectric sensor is connected with the high-speed data acquisition card through BNC output and BNC input of the charge amplifier, the high-speed data acquisition card is connected with a control and signal processing and analyzing system, and the piezoelectric sensor is arranged on the surface of a detected workpiece through lubricating grease as a coupling agent.
The control and signal processing analysis system comprises:
the control module controls the motion of the mobile platform, the power of the high-frequency optical fiber pulse laser and the switch;
the parameter modulation module is used for carrying out amplitude and frequency dual modulation on the signal, extracting second harmonic, selecting a variable scale coefficient to reduce the signal frequency and carrying out secondary sampling;
the signal noise reduction module is used for carrying out noise reduction processing on the modulated signal to obtain a final second harmonic signal;
and the result display module is used for displaying the received signal and displaying the processing result of the signal noise reduction module.
And the parameter modulation module adopts a genetic algorithm to select an optimal method to carry out amplitude and frequency dual modulation on the signal.
Furthermore, the parameter modulation module firstly extracts second harmonic through FFT band-pass filtering, selects variable scale coefficient to reduce signal frequency for secondary sampling, then carries out amplitude and frequency dual modulation before the signal is input into the signal noise reduction module, and inputs the signal into the signal noise reduction module to carry out signal-to-noise ratio improvement processing on the signal after adopting a genetic algorithm to calculate optimal modulation parameters.
Further, the signal noise reduction module inputs the modulated signal into a stochastic resonance principle bistable system for noise reduction processing to obtain a final second harmonic signal.
The phased array nonlinear laser ultrasonic detection system provided by the invention has the specific steps of detecting a workpiece to be detected, and comprises the following steps:
s1: the method is characterized in that an ultrasonic probe is fixed on the surface of a workpiece to be detected by adopting a coupling agent, and the laser is scanned or focused in different ranges according to phased array control sound beams, or the laser is controlled to scan the path of a series of point light sources for global scanning.
S2: the control high-frequency optical fiber pulse laser excited laser is divided into a plurality of light paths by a beam splitter, is controlled by a phase controller and a scanning voltage controller, and is excited by delaying the excitation pulse at the same time to form a phased array scanning path formed by point light sources, so that the deflection and focusing of ultrasonic sound beams at any angle are completed, and the detection of surface defects and the detection of defects at different depths in the interior are realized.
S3: the measured workpiece is placed on the moving platform, the focal length of the high-frequency fiber laser to reach the best point source is set before an experiment, the distance between the measured workpiece and the high-frequency fiber laser is measured through the laser range finder, and accurate focusing of the high-frequency fiber laser is achieved.
S4: setting the center frequency of the pressure sensor, the sampling frequency of the high-speed data acquisition card and the upper limit cut-off frequency and the lower limit cut-off frequency of FFF (frequency filter function) band-pass filtering, and receiving ultrasonic sound beam signals sent by the laser ultrasonic transmitting system.
S5: after the result display module displays the received signals, the parameter modulation module extracts second harmonic waves by adopting FFT band-pass filtering, selects a variable scale coefficient for secondary sampling, calculates optimal modulation parameters by adopting a genetic algorithm, inputs the optimal modulation parameters into a stochastic resonance bistable system to improve the signal-to-noise ratio of the signals, finally obtains second harmonic wave signals by adopting the variable scale coefficient, and realizes the detection of the material performance and the state by analyzing the signals.
Furthermore, the radius of an excited light spot of the high-frequency fiber pulse laser is 0.5mm, the upper limit cutoff frequency of the FFF band-pass filtering is 3MHz, the lower limit cutoff frequency is 0.4MH, and the sampling frequency of the high-speed data acquisition card is 30 MHz.
Compared with the prior art, the phased array nonlinear laser ultrasonic detection system provided by the invention at least has the following beneficial effects:
1) the invention adopts the phased array technology, the phased array technology can realize the focusing of multiple sound beams and the more accurate and rapid positioning of the defects by rapid scanning, the more comprehensive and accurate detection of the surface and internal defects can be realized, and the resolution ratio of the cracks with small size can be detected by adopting the second harmonic technology;
2) the random resonance principle is adopted, namely, a useful signal to be detected is enhanced by using a noise signal, a part of low-frequency noise energy can be converted into signal energy, the signal energy is enhanced while the noise energy is weakened, so that weak signal detection is realized, and the same-frequency separation and the rapid calculation can be realized;
3) the use of a piezoelectric sensor as a receive signal is more sensitive than an optical interferometer;
4) the automatic distance adjusting and focusing function of the laser distance meter is used for measuring the distance, so that the operation is more convenient and faster;
5) and a high-frequency pulse laser is adopted, so that the resolution ratio is higher, the accuracy is higher, and the method is more suitable for industrial application.
Drawings
FIG. 1 is a schematic structural diagram of a phased array nonlinear laser ultrasonic inspection system in an embodiment;
FIG. 2 is a schematic diagram of the laser phased array principle in the embodiment;
FIG. 3 is a flowchart illustrating signal processing performed by the PC according to an embodiment after receiving a signal;
FIG. 4 is a schematic flow chart of the genetic algorithm in the examples.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
Examples
The invention relates to a phased array nonlinear laser ultrasonic detection system, which is used for carrying out nonlinear laser ultrasonic detection on a workpiece to be detected on a moving platform, wherein the moving platform is provided with a motor, and the system comprises a laser ultrasonic transmitting system, an ultrasonic receiving system and a control and signal processing analysis system. As shown in figure 1 of the drawings, in which,
the laser ultrasonic transmitting system comprises a high-frequency optical fiber pulse laser, a beam splitter, a phase controller and a scanning voltage controller. The high-frequency optical fiber pulse laser is connected with the beam splitter, the beam splitter is connected with the phase controller, one end of the scanning voltage controller is connected with the phase controller, and the other end of the scanning voltage controller is connected with the control and signal processing analysis system. A laser beam excited by a high-frequency optical fiber pulse laser is divided into a plurality of light paths by a beam splitter, is controlled by a phase controller and a scanning voltage controller, and is excited by delaying the excitation pulse at the same time to form a phased array scanning path formed by point light sources, so that the deflection and focusing of ultrasonic sound beams at any angle are completed, and the detection of surface defects and the detection of defects at different depths in the interior are further realized.
In this embodiment, as a preferred scheme, the repetition frequency of the high-frequency fiber pulse laser is 20KHz, and compared with the repetition frequency of the conventional laser ultrasonic YAG pulse laser being 10-20Hz, the high-frequency fiber pulse laser can complete the work more efficiently and accurately on the premise of ensuring normal work.
The ultrasonic receiving system comprises a piezoelectric sensor, a charge amplifier and a high-speed data acquisition card. The piezoelectric sensor is connected with the high-speed data acquisition card through the charge amplifier and is used for completing the real-time acquisition of signals and displaying, processing and analyzing the signals on a PC (personal computer) on the control and signal processing and analyzing system. The piezoelectric sensor is arranged on the surface of a workpiece to be detected by using lubricating grease as a coupling agent. The PC is used for completing hardware control and software analysis, the hardware control comprises power and switch control of the laser, scanning voltage controller control, a mobile platform workbench motor and a high-speed data acquisition card circuit control, the software analysis completes extraction of detection signal second harmonic and further analysis of a noise reduction result, and defect detection with high efficiency, high sensitivity and high resolution is achieved.
As a preferred scheme, the center frequency adopted by the piezoelectric sensor can be selected according to the actual condition of a tested piece, and is connected with a high-speed data acquisition card through the BNC output and the BNC input of the charge amplifier, and the high-speed data acquisition card is connected with a control and signal processing analysis system and used for completing the real-time acquisition of ultrasonic signals.
The hardware control of the control and signal processing analysis system comprises the power and switch control of a laser, the control of a scanning voltage controller, the control of a workbench motor and a data acquisition card circuit. The control and signal processing and analyzing system comprises a control module, a signal noise reduction module, a parameter modulation module and a result display module. The control module is connected with the parameter modulation module, the parameter modulation module is connected with the signal noise reduction module, and the signal noise reduction module is connected with the result display module. The signal noise reduction module adopts a signal noise reduction module of a bistable system based on stochastic resonance principle, and the parameter modulation module adopts a genetic algorithm to select an optimal method for parameter modulation and extracts second harmonic waves for parameter transformation. Specifically, a parameter modulation module acquires a signal obtained by detection in real time, FFT band-pass filtering is carried out to extract second harmonic, a variable scale coefficient is selected to reduce the frequency of the signal for secondary sampling, amplitude and frequency dual modulation is carried out before the signal is input into a bistable system, an optimal modulation parameter is calculated by using a genetic algorithm, the optimal modulation parameter is input into a stochastic resonance bistable system to carry out signal-to-noise ratio improvement on the signal, and finally, the variable scale coefficient is used for obtaining a clearer and more accurate second harmonic signal, so that the detection of tiny defects or closed defects is realized. The control and signal processing and analyzing system can adopt a PC to realize the functions.
Further, the upper cut-off frequency of the band-pass filter is 3MHz, and the lower cut-off frequency is 0.4 MHz.
Further, a function of the modulation signal is used: w (t) ═ Accos(2πfct), carrying out amplitude and frequency dual modulation before signals are input into a bistable system, wherein the preferred selection parameter is the signal amplitude AcSum signal frequency fcThe stochastic resonance detection method aims to effectively utilize noise energy and transfer the noise energy into a useful signal so as to improve the output signal-to-noise ratio (SNR) of a nonlinear system. Therefore, in the process of iteratively searching the double modulation parameters, the genetic algorithm evaluates and screens the quality of individuals in the population by taking the SNR as a fitness function, and reserves high-quality individuals for heredity by taking the SNR as a standard. A binary coding mode is adopted, namely a binary character string {0,1} with the coding length of l is used for representing each chromosome in each generation of population.
Furthermore, a random resonance principle is adopted, namely, a useful signal to be detected is enhanced by using a noise signal, a part of low-frequency noise energy is converted into signal energy, the signal energy is enhanced while the noise energy is weakened, so that weak signal detection is realized, and the same-frequency separation and rapid calculation can be realized.
The specific working process of the phased array nonlinear laser ultrasonic detection system for detection is as follows:
step S1: the workpiece to be detected can be selected from aluminum blocks with any size and any thickness to respectively detect fine or closed cracks and mechanical properties, an ultrasonic probe is fixed on the surface of the material by a coupling agent, if the surface defect is detected, a surface wave probe is used, and if the internal defect is detected, a longitudinal wave probe is used, the scanning or focusing in different ranges is realized by controlling an acoustic beam according to a phased array as shown in figure 2 (the figure is a phased array schematic diagram, and is the prior art, and is not repeated herein), or the laser only needs to scan the path of a series of point light sources when the global scanning is needed.
Step S2: the laser excited laser is divided into a plurality of light paths by a beam splitter, is controlled by a phase controller and a scanning voltage controller, is excited by delaying excitation pulses at the same time to form a phased array scanning path formed by point light sources, completes deflection and focusing of ultrasonic sound beams at any angle to realize detection of surface defects and detection of defects at different depths in the laser excited laser, the radius of the excited light spot is preferably 0.5mm, the power percentage of the laser can be controlled by the controller, and the signal-to-noise ratio is improved on the premise of generating a thermo-elastic effect.
Step S3: the measured workpiece is placed on the moving platform, the distance is measured through the laser range finder before the experiment is started, the focal length of the high-frequency fiber laser reaching the optimal point source is about 160mm, the distance between the object and the laser is measured through the laser range finder, the PC adopts a special stepping motor driver, and the stepping motor driver is connected with a motor of the moving platform. The whole process adopts closed-loop control, and the computer only needs to output two signals to the driver: pulses and direction signals. The frequency of the pulse signal controls the rotating speed of the stepping motor, and the number of the pulses controls the rotating angle of the stepping motor; the direction-adjusting signal controls the steering of the stepping motor, so that the aim of accurate focusing of the laser is fulfilled.
Step S4: in order to realize synchronous triggering and acquisition, the high-frequency optical fiber pulse laser adopts a special triggering channel, the output charge of a charge amplifier is matched with the input charge of a high-speed data acquisition card to finish the real-time transmission of signals, the general sampling frequency is set to be 5-10 times of the maximum frequency of the signals, the acquisition frequency of the acquisition card is 30MHz, the sampling length is set to be 1Ksa, the triggering signals are provided by a controller, the upper limit cut-off frequency and the lower limit cut-off frequency of an FFT band-pass filter are 0.4MHz and 3MHz,
step S5: when the PC displays that the received signal contains multiple modes, which cannot be imaged, and the noise signal caused by the surrounding environment also affects the imaging accuracy, so as shown in fig. 3 and 4, in fig. 3, h (t) represents the original signal; the method comprises the steps of extracting second harmonic by FFT band-pass filtering, selecting a variable scale coefficient for secondary sampling, calculating optimal modulation parameters by using a genetic algorithm, inputting the optimal modulation parameters into a stochastic resonance bistable system to improve the signal-to-noise ratio of signals, obtaining clearer and more accurate second harmonic signals by using the variable scale coefficient, and realizing the detection of material performance and state by analyzing the signals.
The invention adopts the phased array technology, the phased array technology can realize the focusing of multiple sound beams and the more accurate and rapid scanning and positioning of defects, can realize the more comprehensive and accurate detection of surface and internal defects, and the invention adopts the second harmonic technology to detect that the resolution ratio of cracks with small size is higher.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and those skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. The utility model provides a phased array nonlinear laser ultrasonic testing system, includes the moving platform that is used for placing the work piece that is surveyed, its characterized in that still includes:
the laser ultrasonic transmitting system transmits laser to a workpiece to be detected to form a phased array scanning path formed by point light sources so as to finish deflection and focusing of ultrasonic sound beams at any angle;
the ultrasonic receiving system receives an ultrasonic sound beam signal sent by the laser ultrasonic transmitting system and sends the signal to the control and signal processing and analyzing system;
and the control and signal processing and analyzing system controls the laser ultrasonic transmitting system and the mobile platform and processes the received signals to realize defect detection.
2. The phased array nonlinear laser ultrasonic detection system according to claim 1, wherein the laser ultrasonic emission system comprises a high-frequency fiber pulse laser, a beam splitter, a phase controller and a scanning voltage controller, the high-frequency fiber pulse laser is connected with the beam splitter, the beam splitter is connected with the phase controller, one end of the scanning voltage controller is connected with the phase controller, and the other end of the scanning voltage controller is connected with the control and signal processing analysis system.
3. The phased array nonlinear laser ultrasonic detection system according to claim 2, characterized in that the high frequency fiber pulse laser excites a laser beam, the laser beam is divided into a plurality of light paths by a beam splitter, the light paths are controlled by a phase controller and a scanning voltage controller, and excitation pulses are excited at the same time delay to form a phased array scanning path composed of point light sources, so as to complete deflection and focusing of ultrasonic sound beams at any angle.
4. The phased array nonlinear laser ultrasonic inspection system according to claim 1, wherein the ultrasonic receiving system comprises a piezoelectric sensor, a charge amplifier and a high-speed data acquisition card, the piezoelectric sensor is connected with the high-speed data acquisition card through a BNC output and a BNC input of the charge amplifier, the high-speed data acquisition card is connected with a control and signal processing analysis system, and the piezoelectric sensor is placed on the surface of a workpiece to be inspected through lubricating grease as a coupling agent.
5. The phased array nonlinear laser ultrasonic inspection system in accordance with claim 2, wherein said control and signal processing analysis system comprises:
the control module controls the motion of the mobile platform, the power of the high-frequency optical fiber pulse laser and the switch;
the parameter modulation module is used for carrying out amplitude and frequency dual modulation on the signal, extracting second harmonic, selecting a variable scale coefficient to reduce the signal frequency and carrying out secondary sampling;
the signal noise reduction module is used for carrying out noise reduction processing on the modulated signal to obtain a final second harmonic signal;
and the result display module is used for displaying the received signal and displaying the processing result of the signal noise reduction module.
6. The phased array nonlinear laser ultrasonic inspection system in accordance with claim 5, wherein the parameter modulation module employs a genetic algorithm to select an optimal method for dual amplitude and frequency modulation of the signal.
7. The phased array nonlinear laser ultrasonic detection system according to claim 6, wherein the parameter modulation module firstly performs second harmonic extraction through FFT band-pass filtering, selects a variable scale coefficient to reduce signal frequency for secondary sampling, then performs amplitude and frequency dual modulation before the signal is input into the signal noise reduction module, calculates optimal modulation parameters by using a genetic algorithm, and inputs the optimal modulation parameters into the signal noise reduction module to perform signal-to-noise ratio improvement processing on the signal.
8. The phased array nonlinear laser ultrasonic testing system according to claim 5, wherein the signal noise reduction module inputs the modulated signal into a stochastic resonance principle bistable system for noise reduction processing to obtain a final second harmonic signal.
9. The phased array nonlinear laser ultrasonic detection system according to any one of claims 1 to 8, wherein the specific steps of the system for detecting a workpiece to be detected comprise:
1) fixing an ultrasonic probe on the surface of a workpiece to be detected by adopting a coupling agent, and controlling an acoustic beam to scan or focus laser in different ranges according to a phased array or controlling the laser to scan the path of a series of point light sources for global scanning;
2) controlling excitation laser of a high-frequency fiber pulse laser to be divided into a plurality of light paths by a beam splitter, controlling the light paths by a phase controller and a scanning voltage controller, delaying excitation pulse excitation at the same time to form a phased array scanning path formed by point light sources, and completing deflection and focusing of ultrasonic sound beams at any angle so as to realize detection of surface defects and detection of defects at different depths in the interior;
3) placing a workpiece to be measured on a moving platform, setting a high-frequency fiber laser to reach the focal length of an optimal point source before an experiment, and measuring the distance between the workpiece to be measured and the high-frequency fiber laser through a laser range finder to realize the accurate focusing of the high-frequency fiber laser;
4) setting the center frequency of a pressure sensor, the sampling frequency of a high-speed data acquisition card and the upper limit cut-off frequency and the lower limit cut-off frequency of FFF (frequency-filter function) band-pass filtering, and receiving an ultrasonic sound beam signal sent by a laser ultrasonic transmitting system;
5) after the result display module displays the received signals, the parameter modulation module extracts second harmonic waves by adopting FFT band-pass filtering, selects a variable scale coefficient for secondary sampling, calculates optimal modulation parameters by adopting a genetic algorithm, inputs the optimal modulation parameters into a stochastic resonance bistable system to improve the signal-to-noise ratio of the signals, finally obtains second harmonic wave signals by adopting the variable scale coefficient, and realizes the detection of the material performance and the state by analyzing the signals.
10. The phased array nonlinear laser ultrasonic testing system according to claim 9, wherein the radius of an excited light spot of the high-frequency fiber pulse laser is 0.5mm, the upper limit cutoff frequency of the FFF band-pass filter is 3MHz, the lower limit cutoff frequency is 0.4MH, and the sampling frequency of the high-speed data acquisition card is 30 MHz.
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